Watchstrap clasp

ABSTRACT

A clasp fastener having a clasp (1) is designed to be snapped into engagement by exerting a closing force. A locking device (4) for locking the clasp (1) is placed by the closing force in an engaged position in which it is in a first snap engagement with a locking projection (6), and a closing member (5) for closing the clasp (1) is fixed by the closing force in a safety position in which it is in a second snap engagement with the locking device (4) so that the snapping force of the first engagement of the clasp (1) with the locking projection (6) is increased. At least one variable-diameter pin (17,18) that is flexible and/or has different diameters allows some movement of the locking device (4), so that the effective closing force exerted on the locking projection (6) is reduced.

FIELD OF THE INVENTION

This invention relates to fasteners and more particularly to a safetyclasp fastener for a watch strap or bracelet.

BACKGROUND OF THE INVENTION

Usually, straps of wrist-watches are opened and fastened by using knownfastener devices like a buckle or a clasp. The application of one ofthese fastener devices depends often on the material from which thewatch strap is made. For example, a watch strap made from soft materiallike leather is fastened by actuating a buckle. By contrast, a watchstrap made from rigid or metallic material is often fastened by snappinga clasp.

A watch strap having a buckle is fastened in several stages. First, anend portion of the watch strap is inserted into a first loop, then atongue of the buckle is engaged in a strap hole and finally the buckleis fixed by inserting the end portion of the watch strap into a secondloop of the buckle. The end portion is secured by sliding its end in aguide loop of the watch strap. A watch strap having a clasp, bycontrast, is snapped in one or two stages by fixing the clasp to a studof the watch strap.

Hereinafter, discussion will be limited to the advantages anddisadvantages of a clasp fastener of a watch strap.

A clasp fastener is generally provided with an adjusted closing force.Usually, the closing force is regulated during manufacture and isadjustable by a specialist during maintenance of the watch strap. Thisforce can differ in function of the watch strap model chosen. Modelsdestined for male or sporting users are activated with a closing forcehigher than that of a model destined for female users. One disadvantageis that the closing force of a watch strap clasp cannot be regulated byusers as a function of daily or leisure activities.

A clasp fastener which is not provided with a security device forsecuring its fastening procedure, can, in accordance with the strengthof the closing force, open as the result of a heavy shock, for exampleduring a sport activity. One disadvantage is that a watch strap clasphaving no security device cannot prevent unintentional fastener opening.

SUMMARY OF THE INVENTION

An object of the invention is to provide a clasp fastener with generalapplication, for example for a wrist-watch, which has a particularlycompact construction and is compatible with known, proven manufacturingmethods.

According to the invention, this object is achieved by a clasp fastenerwith a completely novel concept. The clasp fastener is made fromelements which allow positioning and securing or safety engagement ofthe clasp and which allow individual regulation of the closing force.

By a latching force, in a first stage, a locking device of the claspcarries out a positioning closure, i.e., the actuation of the lockingdevice allows its positioning against a locking projection of the clasp(first snap engagement). In a second stage, a security cover of theclasp carries out a securing closure, i.e., the clasp is fixed by thesecuring cover (second snap engagement), increasing therefore thelatching force of the first snap engagement of the clasp with thelocking projection.

Moreover, one or more variable-diameter pins of the locking device areprovided, these pins having spring characteristics and/or differentdiameters for allowing some movement or clearance relative to one ormore locking elements of the locking device, reducing therefore theclosing force effectively exerted on the locking projection and allowingindividual regulation of the closing force.

Finally, the securing cover is mounted in a detachable manner about anaxis of articulation of a hinge. One or more locking elements havingstraight and rigid portions constitute a resisting axis, which axisresists closure of the security cover in a closure plane. The one ormore locking devices are adjustable with respect to the hinge, so as tobe able to vary the mutual distance from the straight and rigid portionsto the hinge for increasing or reducing the resisting force. Thisresisting force resists the securing closure of the security cover onthe locking device, allowing individual regulation of the latchingforce.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and advantages of the invention will be betterunderstood from the following description with reference to severalpreferred embodiments, shown in the attached drawings, wherein:

FIGS. 1a and 1b are perspective views of a preferred embodiment of aclasp fastener;

FIG. 2 is a perspective, exploded view of the preferred embodiment of aclasp fastener according to FIGS. 1a and 1b;

FIGS. 3a and 3b are front and side elevations of a first preferredembodiment of a locking device of a clasp fastener;

FIG. 4a is a perspective, exploded view of the preferred embodiment of alocking device of a clasp fastener according to FIGS. 3a and 3b;

FIGS. 4b and 4c are sectional views of a preferred embodiment of asecuring cover of a clasp fastener according to FIGS. 1a, 1b and 2;

FIGS. 5a to 5c are sectional views of a preferred embodiment of a claspfastener according to FIGS. 3a, 3b and 4 showing different stages ofoperation of the closure mechanism;

FIGS. 6a and 6b are a longitudinal view and sectional view of a secondpreferred embodiment of a clasp fastener; and

FIG. 7 is a transverse sectional view of a second preferred embodimentof a clasp fastener according to FIGS. 6a and 6b.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1a and 1b show a preferred embodiment of a clasp fastener, forexample for a wrist watch, in a perspective view with a watch strap, ina closed state (FIG. 1a) and in an open state (FIG. 1b). FIG. 2 is aperspective, exploded view of the elements of the clasp fastener. Thewatch strap and the visible elements of the clasp fastener arepreferably made from metal. They are, for example, constructed fromstainless steel and/or gold. The partial views according to FIGS. 1a, 1band 2 essentially show a clasp fastener, final links 2, 2' of the strap,a lower or base strip 3 of the clasp, a locking projection 6 mounted,for example by welding, on lower strip 3 of the clasp, a joining piece 7which acts as a terminal connection element of the clasp, an upper strip11 of clasp 1 and a locking device 4 provided with a securing cover 5 ofclasp 1. With the knowledge of the present invention, a person skilledin the art can implement other embodiments of a clasp fastener.

Clasp 1 is mounted in an openable manner about three articulation axesof three rods 8, 9 and 10 forming hinges. Rod 8 forms a hinge whichallows articulation between upper strip 11 of clasp 1 and lower strip 3of the clasp. Rod 9 forms a hinge which allows articulation betweenlocking device 4 and a bushing 9.0 having a guiding function and beingfixed to upper strip 11 of clasp 1. Rod 10 forms a hinge allowingarticulation between securing cover 5 and locking device 4 and alsobetween locking device 4 and final link 2' of the watch strap orbracelet. Clasp 1 can be latched closed by successive snap engagementsof locking device 4 and securing cover 5 with locking projection 6.Completing the description of the visible elements, a rod 13 forms ahinge 13 allowing articulation between joining piece 7 and a final link2 at the other end of the watch strap or bracelet. The axes of the rodsforming hinges 8, 9, 10 and 13 are oriented more or less perpendicularto the general plane of the watch strap and to the opening and closureplanes of clasp 1. With the knowledge of the present invention, a personskilled in the art can implement other arrangements of axes of a claspfastener.

According to one characteristic of the invention, the snapping mechanismof the watch strap clasp fastener operates by means of articulationelements which are activated in two engagement stages in a closure planeof clasp 1. In a first stage, for example, by pressing an end portion ofsecuring cover 5, upper strip 11 of clasp 1 is pivoted relative to finallink 2' until upper strip 11 contacts against lower strip 3 of theclasp. At the same time, locking device 4 is pressed against lower strip3 of the clasp until locking device 4 contacts locking projection 6which protrudes from lower strip 3 through an opening in upper strip 11of clasp 1. Locking device 4 is positioned by a first snap engagementagainst locking projection 6. In a second stage, securing cover 5 ispivoted relative to locking device 4 and pressed against locking device4. Securing cover 5 is kept on locking device 4 by a second snapengagement. This second snap engagement increases the snapping force ofthe first snap engagement of clasp 1 with locking projection 6. Clasp 1according to the invention is, therefore, engaged in a secured closurestate. Details concerning these engagements are described in thedescription of FIGS. 5a to 5c, 6a, 6b and 7.

Securing cover 5 is a closure device of the clasp fastener and anadornment piece. The aim is to hide locking device 4 under securingcover 5. In the closed state of the clasp, securing cover 5 covers andhides locking device 4 more or less completely. Closed clasp 1 with anengaged securing cover 5 has a similar appearance as joining piece 7 andimproves appearance. The presence of a crown on the external wall ofsecuring cover 5 leads to a further increase of the very attractiveappearance of clasp 1.

The opening mechanism of the closed watch strap clasp is identical tothe closure mechanism, the above described two stages simply must bereversed. The opening occurs by actuating locking device 4. According toa preferred embodiment, securing cover 5 is first lifted by placing athumb or an index finger in a groove or recess 12 in the external wallof joining piece 7 and next to a crown on the external wall of securingcover 5, lifting the cover. With the knowledge of the present invention,a person skilled in the art can implement other arrangements of thiskind of clasp fasteners.

FIGS. 3a and 3b show a first preferred embodiment of a locking device 4of a clasp fastener in a top plan view parallel with a longitudinalplane (FIG. 3a) and in a side elevation view showing a lateral profile(FIG. 3b). FIG. 4a is a corresponding perspective, exploded view.Locking device 4 comprises a case 4.0 with a central notch 16. Case 4.0has through-holes 14.0, 14.0' forming bushings aligned with each otherand having a guide function for keeping axes of two locking elements 14,14' aligned. Case 4.0 is also penetrated by aligned holes 10.0, 10.0'for receiving rod 10 coaxially with the holes (see the description ofFIGS. 1a, 1b and 2). According to a preferred embodiment, two guidebushings 15, 15' support rod 9 of the hinge previously described in aguide bushing 9.0 welded on upper strip 11 of clasp 1 (see thedescription of FIGS. 1a, 1b and 2). With the knowledge of the presentinvention, a person skilled in the art can implement other arrangementsof elements of a clasp fastener. For example, it is possible to realizea clasp fastener having only one locking element.

According to the first preferred embodiment of a clasp fastener, the twolocking elements 14, 14' are elongated contact bolts having contactforces exerted along an axis AA' (FIG. 4a). The locking elementscomprise, for example, springs. The contacting force of locking elements14, 14' is defined by the chosen dimensions (length, diameter, etc.) andby the materials chosen. Each locking element 14, 14' comprises a outerbolt 14.1, 14.1' and an inner bolt 14.2, 14.2'. Outer bolts 14.1, 14.1'are each provided with a rounded and convex portion for contact purposesand with an elongated portion for sliding and pivot purposes. Innerbolts 14.2, 14.2' are each provided with a rounded and convex portionfor contact purposes. Outer bolts 14.1, 14.1' and inner bolts 14.2,14.2' are joined in a way to resist compressive forces along theircontact axis AA'. After mounting in case 4.0 of locking device 4,locking elements 14, 14' are guided by holes 14.0, 14.0' having aguidance function and being able to support external pressure exerted onouter bolts 14.1, 14.1' and on inner bolts 14.2, 14.2'. Locking elements14, 14' are mounted in a detachable manner and with some movement orclearance along their contact axis AA'. Outer bolts 14.1, 14.1' protrudebeyond two external walls of case 4.0, while inner bolts 14.2, 14.2'protrude inwardly beyond two internal walls of case 4.0. Thus, endportions of locking elements 14, 14' protrude beyond two external wallsof locking device 4 on the side of contact with securing cover 5, whileinner end portions of locking elements 14, 14' protrude beyond twointernal walls of locking device 4 to make contact with lockingprojection 6. Once locking device 4 is engaged with locking projection6, projection 6 is within central notch 16 in engaged contact withlocking elements 14, 14'. After engagement of securing cover 5 withlocking device 4, walls 22, 22' and recesses 20, 20' of securing cover 5are in engaged contact with locking elements 14, 14'. A preferredembodiment of a securing cover 5 is shown in FIGS. 5a to 5c. Detailsconcerning the functioning of locking elements 14, 14' are describedwith reference to FIGS. 5a to 5c.

The stages of the closure and opening mechanism in a closure and openingplane of a first preferred embodiment of locking device 4 of a claspfastener are shown in three different states in FIGS. 5a to 5c. FIGS. 5ato 5c are sectional views showing partly a locking projection 6,securing cover 5, and a locking device 4 having two locking elements 14,14' mounted in two guide holes 14.0, 14.0' which keep the lockingelements coaxial, the locking elements 14, 14' each having an outer bolt14.1, 14.1' and a inner bolt 14.2, 14.2'.

FIG. 5a shows a first state of the closure stages. According to onecharacteristic of the invention, locking projection 6 welded on lowerstrip 3 of the clasp is provided with two fixing recesses 6.0, 6.0'having concave surfaces. Fixing recesses 6.0, 6.0' serve for snapengagement of the rounded, convex portions of inner bolts 14.2, 14.2'.Preferably, the concave surfaces of fixing recesses 6.0, 6.0' and theconvex surfaces of inner bolts 14.2, 14.2' are shaped to match eachother, having for example the same radius, allowing optimized contactdue to a maximal contact surface between these two elements. With theknowledge of the present invention, a person skilled in the art canimplement other embodiments of locking projections.

FIG. 5b shows a second state of the closure stages wherein lockingdevice 4 is positioned by a first snap engagement with lockingprojection 6 (first closure stage). Locking device 4 comprises, withreference to FIG. 4, central notch 16 and inner bolts 14.2, 14.2'protrude through internal walls defining central notch 16. Underexternal pressures, locking elements 14, 14' are axially movable withclearance along their common axis AA'. They are received with clearancein holes 14.0, 14.0' which serve as guide bushings. Locking elements 14,14' are kept correctly centered along the contact axes AA' and in theholes 14.0, 14.0' by elastic rings 21, 21', 21", 21'". These elasticrings are, for example, open spirals made from spring steel. In order toposition locking device 4 against locking projection 6, a first force orpressure is necessary for sliding inner bolts 14.2, 14.2' onto the outerborders of fixing recesses 6.0, 6.0'. This first force pushes thelocking elements 14, 14' slightly to the exterior of case 4.0 andcompresses elastic rings 21', 21" situated next to inner bolts 14.2,14.2'. After having passed the outer borders of the fixing recesses 6.0,6.0', elastic rings 21', 21" expand and inner bolts 14.2,14.2' weaklylatch with locking projection 6. The clasp fastener is engaged andpositioned. This first closing force or closure pressure can beregulated by different means. According to the preferred embodiments, astrip 400 of locking device 4 contacts a contact element, for example,lower strip 3 of the clasp. This force can be varied by usingvariable-diameter pins. The actuation of locking device 4 againstlocking projection 6 and the variation of actuation forces of the claspwill be described in detail in the description of the second preferredembodiment of a clasp fastener according to FIGS. 6a, 6b and 7.

FIG. 5c shows a third closure state wherein securing cover 5 is kept bya second snap engagement on locking device 4 (second closure stage).With reference to FIGS. 1a, 1b and 2 and to FIGS. 3a, 3b and 4a, 4b and4c, securing cover 5 comprises two internal retaining recesses 20, 20'in side walls 22, 22' for engagement with outer bolts 14.1, 14.1'protruding through external walls of case 4.0. When securing cover 5 isclosed over locking device 4, walls 22, 22' slide over outer bolts 14.1,14.1' and push the locking elements 14, 14' slightly toward the interiorof case 4.0. This second force is chosen to be stronger than theresisting force of elastic rings 21, 21', 21", 21'". As shown in FIG.5c, two elastic rings 21, 21'" situated next to outer bolts 14.1, 14.1'are compressed and that elastic rings 21', 21" situated next to innerbolts 14.2, 14.2' are extended. Inner bolts 14.2, 14.2' lock the fixingrecesses 6.0, 6.0' of locking projection 6. After locking of outer bolts14.1, 14.1' by retaining recesses 20, 20', the elastic rings 21, 21',21", 21'" expand weakly. This second force or pressure increases thesnapping force of the clasp and allows a safety fastening. With theknowledge of the present invention, a person skilled in the art canimplement other embodiments of recess surfaces for successiveengagements of a clasp.

FIGS. 6a and 6b show a second preferred embodiment of a locking device 4of a clasp fastener in a partly sectional outer plan view (FIG. 6a) andin a sectional side elevation (FIG. 6b). FIG. 7 is a transversesectional view. Locking device 4 comprises essentially a case 4.0 with acentral notch 16. Case 4.0 is penetrated by coaxial bore holes 17.0,18.0 which perform a guide function for keeping variable-diameter pins17, 18 along their axis. Moreover, case 4.0 has aligned through-holes10.0, 10.0' for keeping along their axis a rod 10 of a hinge (see thedescription of FIGS. 1a, 1b and 2). According to a preferred embodiment,two guide bushings 15, 15' support a rod 9 of a hinge in a guide bushing9.0 welded onto upper strip 11 of clasp 1. Two locking elements 14, 14'have the shape of elastic, auto-centered clips occupying a space 23within locking device 4. Space 23 is adapted for retaining lockingelements 14, 14'. Once locking device 4 is engaged with lockingprojection 6, the projection is within central notch 16 in engagedcontact with locking elements 14, 14'. After elements 14; 14' protrudebeyond two internal walls of locking device 4 in the area of contactwith locking projection 6. With the knowledge of the present invention,a person skilled in the art can implement other locking elements havingsimilar locking characteristics.

The mechanism of closure and opening of the second embodiment of lockingdevice 4 differs slightly from the first embodiment with two lockingelements 14,14' according to the description of FIGS. 5a to 5c. FIG. 7shows a locking projection 6 screwed into lower strip 3 of the clasp andhaving two fixing recesses 6.0, 6.0' which are concave surfaces of theouter wall of locking projection 6. Fixing recesses 6.0, 6.0' serve topermit snap engagement of the rounded and convex portions of lockingelements 14, 14' having the shape of elastic, auto-centered clips.Preferably, the concave surfaces of fixing recesses 6.0, 6.0' and theconvex surfaces of the locking elements 14, 14' are shaped to match eachother, having for example the same radius allowing optimized contact dueto a maximal contact surface between these two elements. When lockingdevice 4 is positioned against locking projection 6, a first force orpressure is necessary for pushing locking elements 14, 14' into recesses6.0, 6.0'. Clasp 1 is engaged after this first closure stage. The safetyclosure occurs during a second closure stage, i.e., during a second snapengagement of securing cover 5 with locking device 4. With reference toFIGS. 1a, 1b and 2 and to FIGS. 3a, 3b and 4a, 4b and 4c, securing cover5 is engaged with locking elements 14, 14' engagement of securing cover5 with locking device 4, the walls of securing cover 5 are in engagedcontact with locking elements 14, 14'. With the knowledge of the presentinvention, a person skilled in the art can implement other embodimentsof elements of a clasp fastener. For example, it is possible to realizea clasp fastener having only one locking element.

According to the second embodiment, two locking elements 14, 14' eachhaving the shape of an elastic, auto-centered clip, are curved supports,supporting along a contact axis AA' and being provided with curved andmore flexible portions 14.3, 14.3' and with straight and more rigidportions 14.4, 14.4'. These supports have rounded surfaces. Lockingelements 14, 14' are, for example, springs. The contacting force oflocking elements 14, 14' is defined by the chosen dimensions (length,diameter, etc.) and by the materials chosen. Preferably, the spring-likelocking elements 14, 14' have no tension in their uncompressedpositions. After mounting in case 4.0 of the locking device 4, lockingelements 14, 14' are guided in an adjustable manner by the wallsdelimiting space 23. The walls of case 4.0 being next to straightportions 14.4, 14.4' of locking elements 14,14' are, for example,guides. Under the influence of external pressures, locking elements 14,14' are compressible/extendible along their contact axis AA'. Endportions of locking elements 14, 14' protrude beyond two external wallsof locking device 4 on the sides of contact with securing cover 5, whileend portions of locking which protrude through external walls of case4.0 and are compressed. This second force is chosen stronger than theresisting force of locking elements 14, 14' for thereby increasing thepressure against locking projection 6 and allowing a safety closure. Thetotality of these forces or pressures is controllable and variable.

These forces or pressures can be regulated by different means. Accordingto a preferred embodiment, case 4.0 contacts a contact element, forexample, the lower strip 3 of the clasp. The closing force can be variedby means of variable-diameter pins 17, 18. According to onecharacteristic of the invention, these variable-diameter pins areadjustable by the choice of the used material, by the choice of the pindiameter, by the outer surface geometry, etc. These pins are, forexample, soft or they have different diameters. FIG. 7 illustrates anexample of two variable-diameter pins 17, 18, wherein the centraldiameter of variable-diameter pin 17 is smaller than the centraldiameter of variable-diameter pin 18. Locking element 14 is in contactwith clearance with central diameter of variable-diameter pin 17, thelocking element 14' is in contact with little or no clearance with thecentral diameter of variable-diameter pin 18. By a closing force, thediameter of variable-diameter pin 17 allows, therefore, a clearance forlocking element 14, while the constant diameter of variable-diameter pin18 allows little or no clearance with locking element 14'. Such avariation reduces the closing force effectively exerted on lockingprojection 6. With the knowledge of the present invention, a personskilled in the art can provide one or more locking elements having anequal closing force for the clasp.

As a result, the closing force of a clasp provided, for example, with apair of variable-diameter pins 17 (allowing a high variation) is lowerthan the closing force of a clasp provided with a pair ofvariable-diameter pins 18 (allowing a low variation). By using pins 18with a lower variation it is therefore possible to obtain models "Man"or "Sport" destined for male or sporting users are activated having aclosing force higher than that of a model "Women" destined for femaleusers and which are realized by using pins 17 with a reduced centraldiameter for a higher variation. The provision of one or morevariable-diameter pins 17, 18 is not restricted to a clasp 1 accordingto the second embodiment of a locking device 4. This kind of applicationof variable-diameter pins is also and without any problems possible fora clasp 1 according to the first embodiment of a locking device 4.

The closing forces or pressures can be varied not only by usingvariable-diameter pins 17, 18 but they can also be varied by using othervariation means. Another variation means represents the resisting forceof locking elements 14, 14' exerted on securing cover 5 during a safetyclosure in a closure plane over a locking device 4. According to anothercharacteristic of the invention, the orientation of locking elements 14,14' in space 23 of the second embodiment of a locking device 4 isadjustable. Locking elements 14, 14' can, for example, be rotated by180° in space 23. The latter must be designed in a symmetric manner inlocking device 4. Such a 180° rotation allows variation of the mutualdistances between straight portions 14.4, 14.4' of locking elements 14,14' and hinge rod 10. These straight and rigid portions 14.4, 14.4' oflocking elements 14, 14' constitute a resisting axis oriented more orless perpendicular to the closure plane of securing cover 5. Theresisting force of rigid portions 14.4, 14.4' exerted on securing cover5 is increased or reduced as a function of the size of the distancebetween hinge rod 10 and the resisting axis. By rotating lockingelements 14, 14' in space 23, it is therefore possible to vary, i.e., toincrease or to decrease the resisting force exerted on the safetyclosure of securing cover 5. A change in orientation of locking elements14, 14' in space 23 according to FIG. 6a allows, therefore, a variationof the second snap engagement made by the securing cover 5. The firstsnap engagement made by the locking device 4 remains unchanged. The usercan therefore adjust the safety force of clasp 1 in a free and rapidmanner without consultation of a specialist, i.e., according to daily orleisure activities.

The visible elements of the clasp are preferably made from metal, forexample, from stainless steel and/or gold. According to onecharacteristic of the invention, and with reference to the descriptionof FIGS. 1a, 1b, 2, 6b and 7, locking projection 6 is mounted on lowerstrip 3 of the clasp preferably by welding or screwing. Other connectionmethods are naturally possible. Taking into account the high precisionwhich is required for allowing easy and repeated operation of the clasp,and taking into account the difficulties resulting from the treatment ofthe chosen materials (reduced hardening after welding, asymmetricdeformation after welding), preferably, welding is used for fixing alocking projection 6 made from gold on a lower strip 3 made from goldand screwing is used for fixing a locking projection 6 made fromstainless steel on a lower strip 3 made from stainless steel. With theknowledge of the present invention, a person skilled in the art canprovide fixation means for other base materials for example thermofusionfor synthetic thermofusible materials.

What is claimed is:
 1. A clasp fastener having a clasp (1) adapted to beclosed in response to application of a closing force comprisinga basehaving a locking projection; a locking device (4) movable relative tosaid locking projection between an open position and a closed position;said locking device including means for engaging said projection in saidclosed position with a latching force and being movable into said closedposition by application of said closing force; and a securing cover (5)movable by said closing force to a safety position in which said coverengages said locking device (4) and increases said latching force ofengagement of said means for engaging said locking projection (6). 2.The clasp fastener according to claim 1 wherein said means for engagingincludes at least one locking pin (14, 14') movable with clearance alongan axis (AA') to exert said latching force on said locking projection(6).
 3. The clasp fastener according to claim 1 wherein said means forengaging includes at least one locking element (14,14') comprising anelastic, auto-centered clip compressible and extendible along a contactaxis (AA') by said closing force and exerting said latching force onsaid locking projection (6).
 4. The clasp fastener according to claim 3wherein said means for engaging comprises at least one variable-diameterpin (17,18) allowing movement of at least one locking element (14,14')and reducing the effective latching force exerted on said lockingprojection (6).
 5. The clasp fastener according to claim 2 wherein saidlocking device includes a case (4.0) and said at least one locking pincomprises outer bolts (14.1, 14.1') protruding through external walls ofsaid case (4.0) of the locking device (4) in an area of contact withsaid securing cover (5), and inner bolts (14.2, 14.2') protrudingthrough inner walls of said case (4.0) of the locking device in an areaof contact with said locking projection (6).
 6. The clasp fasteneraccording to claim 5 comprising elastic rings (21, 21', 21", 21'") forcentering locking elements (14, 14') along a contact axis (AA') andwherein holes (14.0, 14.0') in said case (4.0) are guide supports andwherein said elastic rings (21, 21', 21", 21'") are compressible andextendible allowing said locking elements (14, 14') to engage recesses(6.0, 6.0') in said locking projection (6).
 7. The clasp fasteneraccording to claim 5 wherein said locking elements (14, 14') are pushedby said closing force and by walls (22, 22') of said securing cover (5)toward an interior of said case (4.0) for engaging the locking elements(14,14') in said safety position in recesses (6.0, 6.0') in said lockingprojection (6) and in recesses (20, 20') in said securing cover (5). 8.The clasp fastener according to claim 3 wherein said securing cover (5)comprises walls defining an enclosed space (23) containing said at leastone locking element, said walls guiding said at least one lockingelement (4) and wherein said at least one locking element has straightand rigid portions (14.4,14.4') defining a resisting axis resistingclosure of said securing cover (5), said at least one locking element(14,14') protruding through outwardly facing walls of said case (4.0) inan area of contact with said securing cover (5), and said lockingelements (14,14') protruding through inwardly facing walls of said case(4.0) in an area of contact with said locking projection (6).
 9. Theclasp fastener according to claim 8 wherein said at least one lockingelement is compressed by said closing force and by walls (22, 22') ofsaid securing cover (5) into a safety position in recesses (6.0, 6.0')of said locking projection (6) and in recesses (20,20') of said securingcover (5).
 10. The clasp fastener according to claim 8 wherein saidsecuring cover (5) pivots around an articulation axis of a hinge andwherein a mutual distance between straight and rigid portions(14.4,14.4') of said at least one locking element and said hinge isadjustable by rotating said at least one locking element (14,14') insaid space (23) for increasing or reducing the force resisting safetyclosure of said securing cover (5) over said locking device (4).
 11. Theclasp fastener according to claim 1 used for closing a clasp fastener ofa wrist-watch strap comprising at least one of gold and stainless steel.12. The clasp fastener according to claim 1 wherein said lockingprojection (6) is mounted on said lower strip (3) by welding orscrewing.